This invention relates to apparatus for generating and modifying video signals. The invention is described embodied in a symbol generator but may also be included in character generators, video graphics devices, paint systems, animation systems and video special effects devices. One type of symbol generator is comprised of a series of stages that define a signal processing pipeline which regenerates a complete desired video color signal each field. That system does not include the capability to provide a color blended symbol or symbol in which the color gradually changes from one area to another. It is a goal to add color blend capability to this type symbol generator without reducing the quality of the output video signal. Another goal is to provide the color blending without limiting the operating rate of the overall symbol generator, and also without requiring an excessive amount of additional circuitry that would substantially increase the cost and complexity of the symbol generator.
Another type of symbol generator utilizes frame buffers to provide and update video signals from one field or frame to the next. Frame buffer systems include separate picture element or storage locations for recording data pertaining to each separate display locations of a video display raster. Frame buffer systems calculate the video signal for each picture element separately and can provide color blends. Specifically, the framebuffer systems processes blocks of data representing portions of a video image each field, formulate vectors, and fill memory blocks of the frame buffer with the desired signal values. Frame buffer systems generally cannot modify a complete video image in real time. The frame buffer design requires a very large amount of data to be processed to provide and update video signals. Complex electronics are needed to identify the portion of the display to be modified and manipulate blocks within the buffer memory representing those portions of the image.